以多条离散曲线为测地线构造离散曲面

为了解决CAD中逆向主动设计问题,提出以任意多条空间离散曲线为测地线构造离散曲面的算法.首先通过密切圆思想离散化曲线相关几何变量;其次利用局部插值思想和测地线蕴涵特征,推导出满足约束条件的离散曲面公式;最后给出以B样条为度量函数的离散曲面构造公式.逆向主动设计实例表明,该算法是可行的并有较强的交互性,可以通过调整B样条度量函数的节点向量或控制顶点来调节曲面形状,设计出满足各种不同需求的曲面,在服装、鞋帽、义齿设计等领域有很好的应用前景.     

B样条曲面的双向插值造型算法

基于Coons-Gordon造型原理,研究了插值两族相交截面线采样点的B样条曲面双向插值造型算法。参数化各采样点并计算每条截面线的节点矢量,估算每条截面线对应的曲面参数,根据每条截面线的节点分布以及另一族截面线对应的曲面参数统一节点矢量。分别插值两族截面线采样点及其公共点得到三张B样条曲面,其布尔和即为插值两族截面线采样点的B样条插值曲面。实例表明,得到的双向插值曲面控制顶点数少,光顺性好。     

集逼近插值于一体的分段3次多项式曲线曲面

为了用一种模型实现逼近与插值的统一,在多项式函数空间上构造了含两组参数的混合函数,并由之定义了基于四点分段的多项式曲线和相应的张量积曲面。当参数取特殊值时,新曲线曲面成为3次均匀B样条曲线曲面。除了继承B样条方法的局部性,自动光滑性等优点之外,新曲线曲面还具有局部形状可调性。限制混合函数中参数的取值范围,可以使新曲线曲面位于控制顶点的凸包内。让混合函数中的一组参数取特定值,可以使新曲线曲面自动插值除边界点以外的控制顶点,且插值曲线曲面的形状依然局部可调。给出了一些曲线曲面图例。     

拟三次三角样条插值曲线与曲面

在构造插值曲线与曲面时,传统的方法多基于多项式函数空间,而基于三角函数空间也能构造插值曲线与曲面.首先基于函数空间Ω =span{1,sint,cost,sin2t,cos2t}构造了一种样条插值曲线与曲面,称之为拟三次三角样条插值曲线与曲面.该曲线与曲面不仅满足C2连续,而且直接插值于给定的控制顶点,避免了通过方程组反求控制顶点.进一步地,为了使所构造的拟三角样条插值曲线与曲面具有局部可调性,利用奇异混合技术在拟三次三角样条插值曲线与曲面中引入了局部形状参数,修改某些形状参数的取值可实现对插值曲线与曲面的局部调整,为样条插值曲线与曲面的构造提供了两种新方法.     

过测地线的调和Bézier曲面设计

极小曲面和测地线是建筑几何领域中2类重要的几何元素,而调和曲面常作为极小曲面的一种线性近似.文中将测地线和调和曲面结合起来,提出一种过给定测地线的调和Bézier曲面设计方法.首先给出了一种构造调和Bézier曲面的新方法,证明了调和Bézier曲面的形状由第一层和第二层的控制顶点完全决定;然后根据测地线的性质,证明了过给定测地线的调和Bézier曲面的形状由该测地线和第二层的首末2个控制顶点完全决定.最后通过若干实例验证了该方法的有效性.文中方法充分利用了测地线和调和曲面的特殊几何性质,对张拉膜建筑结构的几何设计具有一定的实用价值.     

带B样条曲率线的NURBS曲面设计

为了满足产品设计的需要,提出一种NURBS曲面设计算法用于构造插值曲率线的曲面.首先利用给定已知曲线作为公共曲率线的等参曲面束的表达式、B样条的导矢公式和2个B样条的乘积理论,给出以一条非均匀B样条曲线作为公共曲率线的等参曲面束的显式表达式;然后讨论插值曲面可用NURBS精确表示的必要条件,并给出2种表达式,得出以一条非均匀B样条平面曲线作为公共曲率线的曲面束的NURBS精确表达式,以及控制顶点的计算式.通过实例展示了曲面设计效果,表明算法是可行的.     

高阶连续的形状可调三角多项式曲线曲面

目的目前使用的B样条曲线曲面存在着高连续阶与高局部调整性两者无法兼而有之的不足,且B样条曲线曲面的形状被控制顶点和节点向量唯一确定,这些因素影响着B样条方法的几何设计效果与方便性。本文旨在克服这种局限,以期构造具有高次B样条方法的高连续阶,低次B样条方法的高局部调整性,以及有理B样条方法权因子决定的形状调整性的曲线曲面。方法在三角函数空间上构造了一组含参数的调配函数,进而定义具有与3次B样条曲线曲面相同结构的新曲线与张量积曲面。结果新曲线曲面继承了B样条方法的凸包性、对称性、几何不变性等诸多性质。不同的是,同样是基于4点分段,3次均匀B样条曲线C2连续,而对于等距节点,在一般情况下,新曲线C5连续,当参数取特殊值时可达C7连续。新曲线在C5连续的情况下存在1个形状参数,能较好地调整曲线的形状同时又无须改变控制顶点。另外,将形状参数设为特定值,新曲线可以自动插值给定点列。新曲面具有与新曲线相应的优点。结论在强局部性下实现高阶连续性的形状可调分段组合曲线曲面,为高阶光滑曲线曲面的设计提供了可能,并且新曲线实现了逼近与插值的统一表示,能较好地应用于工程实际。调配函数的构造方法具有一般性,可用相同方式构造其他具有类似性质的调配函数。     

利用控制顶点插值的光滑B样条曲线构造方法

针对非均匀采样点拟合时的光滑B样条曲线构造问题,提出一种基于已知控制顶点和节点向量求解未知控制顶点来构造光滑B样条曲线的方法.首先对所有控制顶点进行基函数极值参数化,再将已知控制顶点作为型值点进行光滑样条曲线插值,并在此曲线上通过利用参数化结果求值得到未知控制顶点.该方法通过控制顶点所在曲线的光顺性提高最终生成曲线的连...     

带形状参数三角B样条曲线曲面及其应用

针对样条曲线曲面构造及其在图像放缩中的应用问题,在三角函数空间{1,t,sint,cost,sin2 t,cos2 t}中构造一类带有形状参数的三角B样条基函数,并定义相应的三角B样条曲线和曲面,分析该曲线曲面的性质以及形状参数对曲线曲面形状的调节作用。拓宽形状参数的取值,构造了满足C2连续且可以直接插值控制顶点的三角B样条插值曲线和曲面,并将其应用于图像放缩中。实例说明了所构造的三角B样条曲线曲面在曲线曲面造型和图像放缩方面有较好应用。     

可展曲面上G^2连续的曲线插值方法

根据微分几何理论,给出一种可展曲面上G2连续的曲线插值算法.构造一等距对应将可展曲面展成平面,从而将原问题转化为通常的平面上的曲线插值问题.在R2上利用二次三角B样条曲线插值型值点列,无需反算控制顶点,证明了所得的可展曲面上的插值曲线是G2连续的.理论推导和实例均表明,该算法具有推广应用的广阔前景.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

基于QTE的蒙古文显示机制研究与实现

蒙古语言是中国蒙古族使用的通用语言,由于蒙古文区别于其他文字的书写方式和其自身变形机制等特点,在很多通用的文字处理引擎中都不被支持。在嵌入式产品开发与应用领域中Linux加QTE已经成为流行方式。该文给出了一种在QTE环境上实现基于标准Unicode的蒙古文点阵显示和变形算法, 并自定义了支持蒙古文的QTE组件,扩展了QTE功能,为在Linux加QTE方式的嵌入式体系结构中处理蒙古文提供了一种解决方法。     

基于AD9626的模拟信号采集存储卡设计

自然界的绝大部分信号都是以模拟的形式存在,因此模拟信号的采集转换存储在数字时代十分关键。文章讨论了在雷达信号处理领域基于AD9626的AD采集存储卡的设计原理、硬件结构和程序设计与芯片配置等问题,为今后相关领域的研究提供了可参考的方案。     

A human-computer interface for non-computer specialists

The COM teleconferencing system was designed to be easy to use for both beginners and people with much computer experience. A number of design choices in organizing the human-computer interface were considered very carefully. These design problems are not unique for teleconferencing applications, but will appear in many other developments of human-computer interfaces for non-computer specialists. This report discusses naming conventions, menu format, user commands, help facility and the treatment of ‘type ahead’ from the users.     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

Call for papers Special issue on Modeling and control technologies for civil,energy,and power systems

正The control of civil,energy,and power systems presents significant new challenges for modeling and control theory.The purpose of this special issue is to provide a forum for researchers and practical engineers to discuss the recent advances in modeling and control technology development for civil,energy,and power systems.Prospective authors are invited to submit their original contributions with the focus on theory or applications of modeling,control     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate and promote academic exchange between Chinese and foreign scientists everywhere.